Method for coagulating plastics dispersions using a device with shearing elements

ABSTRACT

Shear forces are used for essentially salt-free coagulation of plastics dispersions or rubber dispersions. For this, method of use is made of an apparatus with at least one shearing module which has a stator and a rotor arranged within the stator, where the surfaces facing toward one another in the stator and in the rotor are in each case smooth, or at least the rotor exhibits a structure formed on its surface and facing from this in the direction of the stator, and between the stator and the rotor there is a gap of predetermined gap width. The process is carried out by passing the dispersion to be coagulated through the gap between stator and rotor and precipitating the dispersion by rotation of the rotor with predetermined shear rate and shear deformation.

The invention relates to the use of an apparatus with at least oneshearing module for essentially salt-free coagulation of plasticsdispersions, and also to the process carried out with this apparatus.

Many polymers are prepared by homo- or copolymerization of suitablemonomers in a liquid medium, e.g. by emulsion, miniemulsion ormicrosuspension poly-merization. Here, the polymer precipitates in theform of a usually aqueous dispersion of solid, from which the polymerhas to be separated out, unless the dispersion is to be used as such.

The polymers are usually separated out from the dispersion bycoagulation. There is a wide variety of different known methods forthis. For example, dispersions can be coagulated by adding strongelectrolytes. This is mostly done using salts which contain polyvalentcations, such as Ca²⁺, Mg²⁺ or Al³⁺. A disadvantage of this method isthat relatively large amounts of precipitating agents remain in theproduct and impair important product properties. Downstream washing ofthe precipitated polymer with large amounts of water is thereforenecessary, and this causes problems in terms of costs and theenvironment. Another disadvantage of precipitation with electrolytes isthat the precipitated product is frequently produced as a clump whichcomprises unprecipitated material or excess precipitating agent, or asvery finely divided material difficult to separate out by sedimentationor filtration.

It has also become known that polymer dispersions can be coagulated bysubjecting them to high shear forces. Here, the respective polymerdispersion is subjected to high shear forces until the polymer particlesagglomerate. If the solids content of the polymer is above 20%, thepolymer coagulated in this way can become pasty to crumbly.

DE-A-196 54 169 discloses a process for coagulating graft-rubberdispersions, where coagulation is brought about usingshear-precipitation in a stator-rotor arrangement. Both the stator andthe rotor, which rotates within the stator, have slots through which thedispersion is passed radially from the inside to the outside as a resultof the rotation of the rotor. The shear to which the dispersion issubjected here is strong enough for it to coagulate.

DE-A-29 17 321 discloses a process for separating out, from an aqueousemulsion, polymers which have a softening range above 100° C., where theaqueous emulsion is coagulated in an extruder by shearing and/or heatingto temperatures above the softening range of the polymer, and thecoagulated material is then melted and discharged hot from the extruder,under pressure. The water is then separated out in a subsequent step.The process is very energy-intensive and requires a counter-rotatingnon-intermeshing twin-screw extruder for the precipitation. In addition,ammonium acetate is used as auxiliary to accelerate the coagulation, andthis is undesirable for environmental reasons.

U.S. Pat. No. 3,821,348 describes a process in whichacrylonitrile-copolymer dispersions or acrylonitrile-graft-polymerdispersions with a high acrylonitrile content and a very low content ofelastomeric butadiene-acrylonitrile rubber are coagulated to give apaste, using a Waring mixer as the shearing apparatus, and then extrudedthrough a fine die to give thin lengths and passed into hot water. Theproduct is then washed, dried and finally shaped into lengths in acompression molder at 150° C.

It is an object of the present invention, in the light of this priorart, to provide an apparatus and a process for coagulating plasticsdispersions or rubber dispersions, with which cost-effective coagulationof dispersions of this type becomes possible without adding chemicalcoagulants.

We have found that this object is achieved by using an apparatus with atleast one shearing module which has a stator and a rotor arranged withinthe stator, where the surfaces facing toward one another in the statorand in the rotor are in each case smooth, or at least the rotor exhibitsa structure formed on its surface and facing from this in the directionof the stator, and between the stator and the rotor there is a gap ofpredetermined gap width.

For the purposes of the present invention, “gap” is a very general andinclusive term for any desired space between rotor and stator. Thepredetermined gap width may therefore also include the flight depth,defined as (outer diameter of a screw minus the diameter of the screwroot)/2.

This apparatus has proven very reliable in the essentially salt-freecoagulation of plastics dispersions or rubber dispersions. It isfundamentally very simple in construction, and no susceptibility toclogging has been found. If desired, additional conveying modules may beused to convey the dispersion to be coagulated to the apparatus and awayfrom the apparatus after coagulation has taken place. However, theapparatus may also be freely operated without conveying modules of thistype. In particular, there is no requirement to use, for example,pressure vessels or pumps to ensure the presence of a certain pressurein advance in order to supply the apparatus with the dispersion to becoagulated.

For the purposes of the present invention, plastics dispersions aredispersions in which the homo- and/or copolymers have a glass transitiontemperature above 0° C., whereas the glass transition temperatures forrubber dispersions are below 0° C.

The predetermined gap width may be constant, but may also in each casevary within each of the one or more shearing modules. The diameter ofthe rotor here may decrease or increase in the direction of conveying.This decrease or increase in the diameter in the direction of conveyingmay occur more than once.

It has proven advantageous for the diameter of the rotor to diminish inthe direction of conveying, or for the predetermined gap width todecrease in the direction of conveying.

The rotor may have a toothed-wheel structure, the rows of teeth in whichhave a circular arrangement radially around the rotor. If desired, thestator may have one or more approximately complementary rows of teeth.In this arrangement the coagulation mechanism is different from thatwith smooth surfaces of the stator and rotor. Whereas in that casecoagulation takes place as a result of exposure to a continuous shearfield, the use of a stator-rotor combination whose rotor has a surfacestructure, or of a stator-rotor combination with complementary toothedwheel or, respectively, rows of teeth gives a constantly repeating shearstress. The dispersion experiences a reduction in pressure once one ofthe rotor teeth has passed by the stator, only to be subjected again tostrong shear at the next tooth which follows. This arrangement givesvery intensive shear action. Depending on the requirements relating tothe dispersion to be coagulated, a selection may thereforeadvantageously be made between a smooth stator-rotor system, i.e. astator-rotor system with a smooth surface, and one in which at least therotor surface has a toothed-wheel structure.

The rows of teeth on the stator and on the rotor may be approximatelyrectangular. They may also have an approximately star-shaped arrangementon the rotor. A helical arrangement of teeth is also possible, but forthis there can be no complementary shaping of the stator.

Upstream and/or downstream of the shearing module of the apparatus usedaccording to the invention, there may be a conveying screw with one ormore flights, preferably arranged on the same shaft as the shearingmodule. The feeding and transport of the dispersion to be coagulated inthe apparatus, and also the to discharge of the coagulated dispersion,can be made to occur of their own accord if a conveying screw is used.

The gap width may vary within a relatively wide range, depending on thedispersion to be coagulated and the product quality desired. Gap widthsof from about 0.05 to 20 mm give good results, and even if the gap widthis in the lower region no susceptibility to clogging of the apparatus isfound. Typical gap widths which may be mentioned for a stator-rotorarrangement with a structured surface are from 0.05 to 20 mm, while fora stator-rotor combination with a smooth surface they are within therange from about 0.3 to 10 mm.

In a preferred use, the shearing module is a screw module, the screw ofwhich forms the rotor. Particular preference is given here to a screw inwhich the diameter of the screw root increase in the direction ofconveying. This of necessity results in a decrease in the predeterminedgap width, i.e. in the flight depth in this case, where the rotor is ascrew. Such a screw module is named a screw having an increasing root.

The shearing module in the form of a screw module simplifies theconstruction of the apparatus used according to the invention, since thescrew can serve simultaneously as conveying screw and as shearingmodule. It has been found that this arrangement can also considerablyreduce the drive power used to transport the plastics dispersion orrubber dispersion to be coagulated, where appropriate in the partiallycoagulated state, through the shearing apparatus.

The invention also provides a process for essentially salt-freecoagulation of plastics dispersions or rubber dispersions using theapparatus described in greater detail above. In this process, thedispersion is passed through the gap between stator and rotor and isprecipitated and subjected to a predetermined shear rate and sheardeformation by rotation of the rotor.

This type of shear precipitation can be carried out without the additionof strong electrolytes, as coagulants, to be dispensed with. The processcan also be carried out continuously.

If the shearing gap is smooth, the decisive parameters for the qualityof the precipitation are the shear rate and, respectively, the sheardeformation.

In a preferred embodiment, the shear rate is from about 100 to 100,000s⁻¹ and the shear deformation is from about 1 to 100,000.

The rotor may rotate at a rotation rate of from about 50 to 10,000 rpm,preferably from about 200 to 8000 rpm. For a stator-rotor combinationwhose surface has a toothed-wheel structure, rotation rates of up to8000 rpm have also proven successful.

The novel process may be used, for example, for coagulating plasticsdispersions and preferably rubber dispersions, composed, for example,of:

from 60 to 100 parts by weight, based on the total weight of thefinished dispersion, of at least one monomer (main monomer) capable ofbeing incorporated by polymerization,

from 0 to 35 parts by weight, preferably from 0 to 20 parts by weight,of at least one functional monomer (comonomer), and

from 0 to 5 parts by weight, preferably from 0 to 3 parts by weight, ofan α,β-unsaturated mono- or dicarboxylic acid.

The main monomer has preferably been selected from the group consistingof:

esters preferably made from α,β-monoethylenically unsaturated mono- ordicarboxylic acids having from 3 to 6 carbon atoms, for example acrylicacid, methacrylic acid, maleic acid, fumaric acid or itaconic acid, andfrom in general C₁-C₁₂ alkanols, preferably C₁-C₈ alkanols and inparticular C₁-C₄ alkanols.

Particular esters of this type are methyl, ethyl, n-butyl, isobutyl,tert-butyl and 2-ethylhexyl acrylates and the correspondingmethacrylates;

vinylaromatic compounds, such as styrene, α-methylstyrene,α-chloro-styrene and vinyltoluenes;

vinyl esters of C₁-C₁₈ mono- or dicarboxylic acids, for example vinylacetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinylstearate;

butadiene.

Particularly preferred main monomers are methyl methacrylate, methylacrylate, n-butyl methacrylate, tert-butyl methacrylate, ethyl acrylate,n-butyl acrylate, 2-ethylhexyl acrylate, styrene and vinyl acetate.

Particularly suitable monomers are:

linear 1-olefins, branched-chain 1-olefins and cyclic olefins, e.g.ethene, propene, butene, isobutene, pentene, cyclopentene, hexene,cyclohexene, octene, 2,4,4-trimethyl-1-pentene, if desired mixed with2,4,4-trimethyl-2-pentene, C₈-C₁₀ olefins, 1-dodecene, C₁₂-C₁₄ olefins,octadecene, 1-eicosene (C₂₀), C₂₀-C₂₄ olefins; oligoolefins preparedwith metallocene catalysis and having a terminal double bond, e.g.oligopropene, oligohexene and oligooctadecene; polyolefins prepared bycationic polymerization with a high proportion of a-olefin, for examplepolyiso-butene. However, it is preferable for no ethene and no linear1-olefin to be incorporated into the polymer.

Acrylonitrile, methacrylonitrile

Vinyl and allyl alkyl ethers having from 1 to 40 carbon atoms in thealkyl radical, where the alkyl radical may also have other substituents,such as hydroxyl, amino or dialkylamino, or they may have one or morealkoxylate groups, for example methyl vinyl ether, ethyl vinyl ether,propyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether,vinyl cyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether,dodecyl vinyl ether, octadecyl vinyl ether, 2-(diethylamino)ethyl vinylether, 2-(di-n-butyl-amino)ethyl vinyl ether, methyldiglycol vinylether, and also the corresponding allyl ethers, and mixtures of these.

Acrylamides and alkyl-substituted acrylamides, e.g. acrylamide,methyl-acrylamide, N-tert-butylacrylamide, N-methyl(meth)acrylamide.

Sulfo-containing monomers, e.g. allylsulfonic acid, methallylsulfonicacid, styrenesulfonate, vinylsulfonic acid, allyloxybenzenesulfonicacid, 2-acryl-amido-2-methylpropanesulfonic acid, and the appropriatealkali metal salts or ammonium salts of these, and mixtures of these,and also sulfopropyl acrylate, sulfopropyl methacrylate.

C₁-C₄-Hydroxyalkyl esters of C₃-C₆ mono- or dicarboxylic acids (seeabove), in particular of acrylic acid, methacrylic acid or maleic acid,or derivatives of these alkoxylated with from 2 to 50 mol of ethyleneoxide, propylene oxide, butylene oxide, or mixtures of these, or esters,with the acids mentioned, of C₁-C₁₈ alcohols alkoxylated with from 2 to50 mol of ethylene oxide, propylene oxide, butylene oxide or mixtures ofthese, for example hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, 1,4-butanediol monoacrylate, ethyldiglycol acrylate,methylpolyglycol acrylate (11 EO), (meth)acrylates of C₁₃/C₁₅oxoalcohols reacted with 3, 5, 7, 10 or 30 mol of ethylene oxide, ormixtures of these.

Vinylphosphonic acid, dimethyl vinylphosphonate and otherphosphorus-containing monomers.

Alkylaminoalkyl (meth)acrylates, alkylaminoalkyl(meth)acrylamides orquaternization products of these, for example 2-(N,N-dimethylamino)ethyl(meth)acrylate, 3-(N,N-dimethylamino)propyl (meth)acrylate,2-(N,N,N-trimethylammonium)ethyl (meth)acrylate chloride,2-dimethyl-aminoethyl(meth)acrylamide,3-dimethylaminopropyl(meth)acrylamide,3-trimethylammoniumpropyl(meth)acrylamide chloride.

Allyl esters of C₁-C₃₀ monocarboxylic acids.

N-Vinyl compounds, such as N-vinylformamide, N-vinyl-N-methylformamide,N-vinylpyrrolidone, N-vinylimidazole, 1-vinyl-2-methylimidazole,1-vinyl-2-methylimidazoline, N-vinylcaprolactam, vinylcarbazole,2-vinylpyridine, 4-vinylpyridine.

Diallyldimethylammonium chloride, vinylidene chloride, vinyl chloride,acrolein, methacrolein.

Monomers containing 1,3-diketo groups, for example acetoacetoxyethyl(meth)acrylate and diacetoneacrylamide, monomers containing urea groups,for example ureidoethyl (meth)acrylate, acrylamidoglycolic acid, methylmethacrylamidoglycolate.

Monomers containing silyl groups, for example trimethoxysilylpropylmethacrylate.

Monomers containing glycidyl groups, for example glycidyl methacrylate.

Dispersions suitable for the novel coagulation process, besides normalemulsions, are in particular graft-rubber dispersions which have beenprepared in aqueous emulsion at least in the final stage of the graftpolymerization, by grafting of the elastomers with the monomers for thegraft shell.

For the purposes of the present invention, graft rubbers are inparticular those graft polymers in which monomers forming hardthermoplastics, for example in particular styrene, acrylonitrile and/ormethyl methacrylate, are grafted as a graft shell onto particle coresmade from soft rubber. This is done by polymerizing or copolymerizingthe monomers for the graft shell in the presence of the rubberparticles. Suitable soft rubbers are elastomeric polymers and/orcopolymers with glass transition temperatures below −10° C., preferablybelow −30° C. Particularly suitable polymers are elastomeric 1,3-dienehomo- and copolymers, such as homo- and copolymers of butadiene,isoprene or chloroprene, preferably butadiene rubber, and alsoelastomeric acrylate homo- and/or copolymers with the low glasstransition temperatures mentioned. Preferred polymers for the graftrubbers coagulated according to the invention are elastomeric acrylatepolymers and 1,3-diene homo- and copolymers, for example homo- andcopolymers of C₄-C₈-alkyl acrylates, in particular of n-butyl acrylateand/or 2-ethylhexyl acrylate. Examples of preferred comonomers for thealkyl acrylates are crosslinking monomers having at least twononconjugated C═C double bonds, for example diallyl maleate, diallylphthalate, diacrylates and dimethacrylates of diols, such as1,4-butanediol or 1,6-hexanediol, etc., and also allyl methacrylate anddihydrodicyclopentadienyl acrylate, used in particular in amounts offrom 0.5 to 10% by weight of the total amount of monomers in theelastomer preparation, and also polar monomers, such as acrylic acid,methacrylic acid, maleic anhydride, acrylamide, methacrylamide,N-methylolacrylamide and -methacrylamide, and alkyl ethers of these. Theproportion of the elastomers in the graft rubber is generally from 30 to85% by weight. The novel process may be used without difficulty tocoagulate graft rubbers whose elastomer proportion is more than 30% byweight, based on the total solids content.

Suitable monomers for polymerizing-on the graft shell are in particularmonomers and mixtures of these which form hard polymers or copolymerswith glass transition temperatures above +50° C. The type of monomer(s)depends here to a large extent on the type of the thermoplastics whichform the polymer matrix after blending with the graft rubber and withwhich the graft shell should have some degree of compatibility oraffinity, in order to achieve a fine two-phase distribution of the graftrubbers in the matrix. Particularly suitable and usual monomers arethose having from 8 to 12 carbon atoms, for example, styrene,α-methylstyrene, and also styrenes and a-methylstyrenes which have oneor more alkyl substituents, in particular methyl substituents, on thebenzene ring. They may be the sole monomers for preparing the graftshell, or be used in a mixture with other monomers, such as methylmethacrylate, methacrylonitrile or preferably acrylonitrile, in whichcase the proportion of methacrylonitrile monomer units and/oracrylonitrile monomer units in the graft shell is from 0 to 45% byweight, preferably from 10 to 40% by weight, of the graft shell.Preference is given to mixtures of styrene with from 10 to 40% by weightof acrylonitrile, based on the total amount of monomers. Other preferredmonomers which may be mentioned for preparing the graft shell aremethacrylates and acrylates, preferably methyl methacrylate, which mayalso be used as sole monomer or as the quantitatively predominantmonomer for preparing the graft shell. Other suitable comonomers forpreparing the graft shell are maleic anhydride, maleimide,N-phenylmaleimide, acrylic acid and methacrylic acid.

Examples of the preparation of dispersions of this type suitable for theapplication of shear precipitation are described, for example, in DE-C-260 135, DE-A-3 22 75 55, DE-A-3 14 93 57, DE-A-3 14 93 58 and DE-A-3 4141 18, which are expressly incorporated herein by way of reference.However, these are in the nature of examples. The application of theshear precipitation according to the invention is not restricted to theexamples of dispersions mentioned here.

More detailed descriptions will now be given of the novel apparatus,using embodiments shown in the drawing, and of the novel process, usingexperimental examples.

FIG. 1 shows a diagram of the novel apparatus with a shearing module.

FIG. 2a-f shows various forms of the rotor showing diagrammatically thetransition from a smooth rotor to a rotor whose surface has a structurewith rows of teeth.

FIG. 3 shows a diagram, partly sectioned, of a shearing module with arotor-stator combination whose surface has a structure with rows ofteeth.

FIG. 4 is a diagram of a rotor with a helical arrangement of teeth.

FIG. 5 is a diagram of the novel apparatus in a version used forExamples 1 to 4.

FIG. 6 is a diagram of the novel apparatus in another version used forExamples 5 to 9.

FIG. 7 is a diagram of the novel apparatus in another version used forExample 18.

FIG. 8 is a diagram of another preferred embodiment of the apparatusused according to the invention with a screw having an increasing rootas rotor.

FIG. 1 is a basic construction diagram for the apparatus used accordingto the invention for essentially salt-free coagulation of plasticsdispersions. A version of the apparatus which has a basic constructionstill further simplified in comparison to this is also described belowwith reference to FIG. 8 from Example 20.

The apparatus of FIG. 1 is composed of a feed zone, indicated overall by1, intended for the dispersion to be coagulated and having a conveyingmodule which is a screw module 2, of the actual shearing zone with theshearing module indicated overall by 3, and of a metering zone,indicated overall by 5 and likewise having a screw module 6. Each of thefeed zone 1 and metering zone 5 is optional and may also therefore beabsent. The shearing module 3 has a fixed cylindrical stator 7 and arotor 9 which is also cylindrical and rotates within the stator 7. Inthe diagram of FIG. 1 both the stator 7 and the rotor 9 have a smoothsurface. Between the stator 7 and the rotor 9 there is a gap 11 whichhas a defined and predetermined gap width.

The dispersion to be coagulated is fed radially into the novelapparatus, either via the feed line 12 into the feed zone 1 and fromthere axially into the shearing module 3 or directly via the feed line12′ (shown here with a broken line) into the gap 11.

If there is a feed zone 1, in the area of which the dispersion is to beintroduced, the latter is then preferably conveyed axially by way of atleast one screw module 2 through the gap 11 formed between the stator 7and the rotor 9. If there is a metering zone 5, downstream conveyingalso preferably takes place by way of at least one screw module 6.

If the dispersion is added via line 12′ directly into the gap 11 it isconveyed by means of an external conveying system, the detail of whichis not shown in FIG. 1, or with the aid of static pressure.

If desired, there may be points for measuring pressure and/ortemperature in the feed zone 1, in the shearing zone formed by theshearing module 3 and/or in the metering zone 5.

Within the shearing module 3, the rotor 9 has been mounted on arotatably mounted shaft not shown in further detail in FIG. 1. Therotation of the rotor 9 subjects the dispersion to shear forcessufficiently high to bring about their coagulation. In the apparatus ofFIG. 1 the gap width is constant. It may, however, also vary within theshearing module 3, and this is brought about by one or more reductionsor increases in the diameter of the rotor 9 in the direction ofconveying.

Each of FIGS. 2a to 2 f show a rotor 9 with a surface structure varyingfrom a smooth surface (FIG. 2a) to a surface structure with rows ofteeth of varying height (FIG. 2c- 2 f). Here, the surface structure onthe rotor 9 is radial rows 13 of teeth in a star-shaped arrangementaround the axis 15 of rotation of the apparatus shown in FIG. 3. Thestator 7 belonging to each of the rotors 9 in FIGS. 2c to 2 f likewisehas the form of a toothed wheel and is composed of rows 13 of teethwhich have a circular arrangement radially around the rotor shaft (notshown) giving an embodiment of the stator 7 which is complementary tothe rotor 9.

This is shown diagrammatically in FIG. 3, where the rotor 9 and thestator 7 in each case have a surface structure in the form of rows 13 ofteeth.

FIG. 4 shows another embodiment of a surface structure for the rotor 9in the form of a helical arrangement of teeth. Here, however, the stator7 always has a smooth surface. As well as the surface structuresdescribed here and shown in the attached FIGS. 2 and 4 for the rotor 9and, where appropriate, for the stator 7, there are many other possibleembodiments. For example, the surface of the rotor 9 may be essentiallysmooth but have a structure in the form of studs, or else the rows ofteeth shown in FIG. 2 may have a diagonal arrangement. The individualteeth may also have a diagonal shape and are then, for example,diamond-shaped instead of rectangular. In each case, the stator 7belonging to the arrangement complements the rotor or is smooth. Thesurface structures described here are merely examples.

The following examples were carried out using apparatus complying withthis general description. In the following, therefore, details are givenonly of modifications to the construction of the apparatus and, whereappropriate, of embodiments of the stator-rotor combination 7, 9.

EXAMPLES 1 TO 4

Preparation of a Graft Rubber

a) Preparation of the Base from Polybutadiene

Butadiene was polymerized in aqueous emulsion, as specified in lines 5to 34 of page 15 of DE-A-31 49 046, which is expressly incorporatedherein by way of reference. The resultant polybutadiene latex had asolids content of about 40% by weight and an average particle size d₅₀of about 80 nm.

b) Agglomeration of the Polybutadiene Base and Grafting withStyrene-acrylonitrile.

50 kg of the polybutadiene latex prepared under a) were the initialcharge in a reactor provided with a stirrer and with a point formeasuring temperature. After heating to about 75° C., 1 kg of anagglomeration latex made from about 96% by weight of ethyl acrylate andabout 4% by weight of methacrylamide (with a solids content of about 10%by weight) was added. This gave a partially agglomerated polybutadienelatex with a bimodal particle size distribution and an average particlesize d₅₀ of 220 nm.

0.2 kg of potassium stearate and 0.025 g of potassium persulfate wereadded at about 75° C. to the latex agglomerated in this way. Afteradding 1.47 kg of styrene and 0.63 kg of acrylonitrile, the mixture waspolymerized for about 15 minutes and then a mixture of 7.35 kg ofstyrene and 3.15 kg of acrylonitrile was added within a period of 3further hours. 0.025 kg of potassium persulfate was then added andstirring was continued at about 75° C. for a further 1.5 hours.

c) Coagulation of the Dispersion Prepared as in a) and b)

The dispersion prepared under a) and b) was coagulated by the novelprocess. The apparatus used for this is shown in FIG. 5. The figuresused to indicate features of the apparatus in FIG. 5 which arecomparable with those in FIG. 1 are higher by 100 than those in FIG. 1.

The apparatus used has no feed zone 1, and the dispersion to becoagulated was therefore added directly and radially into the gap 111 byway of feed line 112′, using a static pressure level prevailing outsidethe apparatus, or using a pump. As shown in FIG. 5, two shearing modules103, 103′ coupled to one another were used, and the dispersion wasconveyed into the first shearing module 103, which is composed of asmooth stator 107 and of a smooth rotor 109 and brings aboutprecoagulation of the dispersion. In this first shearing module 103 thegap width is about 4.5 mm. From there, the dispersion passes onward intothe second shearing module 103′, likewise composed of a smooth stator107′ and of a smooth rotor 109′. Prior to the transition from the firstshearing module 103 to the second shearing module 103′, i.e. in thedirection of conveying, the diameter of the rotor 109 increases.

The gap width of the gap 111′ in the second shearing module 103′ is 0.5or 1 mm and is another area of coagulation. Therefore, only this gapwidth is given in Table 1. The rotation rates for rotor 109 and 109′ aregiven in Table 1. After passing through the second shearing module 103′,the coagulated dispersion is discharged directly without use of ametering zone. The length of each shearing module 103, 103′ is about 90mm, and the diameter of the stator 107 is about 30 mm in the case ofboth of the shearing modules 103, 103′. The other process parameters aregiven in Table 1.

TABLE 1 Experiment Rotation No. Gap width rate Throughput Remarks 1 1 mm2400 rpm 22 kg/h coagulation 2 0.5 mm 2431 rpm 11 kg/h coagulation 3 1mm 1173 rpm 27 kg/h coagulation 4 1 mm  911 rpm 92 kg/h no coagulation

EXAMPLES 5 TO 9

In Examples 5 to 9 described below the method for stages a) and b) ofthe preparation was again as described above in Examples 1 to 4, and theresultant dispersion was coagulated by the novel process. The apparatusused here is shown in FIG. 6. The figures used to indicate featureswhich are comparable with those in FIG. 1 are higher by 200 than thosein FIG. 1.

The apparatus has a feed zone 201 of length about 180 mm, and this areahas a screw module 202 for conveying the dispersion to be coagulated andfed via line 212. This conveys the dispersion into the shearing module203, composed of a smooth stator 207 and a smooth rotor 209, forming agap 211 of gap width about 0.5 mm or 1 mm. The length of the shearingmodule 203 is about 90 mm and the internal diameter of the stator 207 isabout 30 mm. After passing through the shearing module 203, thecoagulated dispersion is discharged directly, without using a meteringzone. Table 2 gives the results of the coagulation, stating in each casethe rotation rate for the rotor 209.

TABLE 2 Experiment Rotation No. Gap width rate Throughput Remarks 5 1 mm5170 rpm 33 kg/h coagulation 6 1 mm 2430 rpm 30 kg/h coagulation 7 1 mm3650 rpm 43 kg/h coagulation 8 0.5 mm 2428 rpm 33 kg/h coagulation 9 0.5mm 1190 rpm 25 kg/h coagulation

EXAMPLES 10 TO 13

The dispersions, which were prepared as stated in Examples 1 to 4 undera) and b) were coagulated in an apparatus corresponding to that showndiagrammatically in FIG. 1. The length of the feed zone 1 here is about90 mm, and it has a conveying screw module 2. Attached to this is theshearing module 3, composed of the smooth stator 7 and the likewisesmooth rotor 9. The gap width of the gap 11 in the shearing module 3 is1 mm. Attached to the shearing module 3 is a metering zone 5 likewisehaving a conveying screw module 6. The dispersion is passed directlyinto the gap 11 of the shearing module 3 and coagulated by exposure tothe shear forces from rotation of the rotor 9 at the rotation ratesgiven in Table 3. The length of the shearing module 3 is about 90 mm andthe internal diameter of the stator 7 is about 30 mm. The results aregiven in Table 3.

TABLE 3 Experiment Rotation No. Gap width rate Throughput Remarks 10 1mm 3660 rpm 20 kg/h coagulation 11 1 mm 2430 rpm 31 kg/h coagulation 121 mm 2420 rpm 42 kg/h coagulation 13 1 mm 3500 rpm 79 kg/h coagulation

EXAMPLES 14 TO 17

Preparation and Coagulation of a Graft-rubber Dispersion withElastomeric Polyacrylate as Graft Base.

a) 160 parts of a mixture made from 98% of butyl acrylate and 2% ofdihydrodicyclopentadienyl acrylate were heated to 60° C. with stirringin 1500 parts of water, with addition of 5 parts of the sodium salt of aC12-C18 paraffinsulfonic acid, 3 parts of potassium peroxodisulfate, 3parts of sodium hydrogencarbonate and 1.5 parts of sodium diphosphate.15 minutes after the start of the polymerization reaction, a further 840parts of the monomer mixture were added within a period of 3 hours.After monomer addition had ended, the emulsion was held at 60° C. forone further hour. The glass transition temperature of the resultantelastomer was −42° C.

2100 parts of the emulsion were mixed with 1150 parts of water and 2.7parts of potassium peroxodisulfate, and heated to 65° C., with stirring.Once this temperature had been reached, 560 parts of a mixture made from75% of styrene and 25% of acrylonitrile were metered in within a periodof 3 hours. After the addition had ended, the mixture was held at about65° C. for about 2 more hours. The glass transition temperature of acopolymer made from 75% of styrene and 25% of acrylonitrile is 111° C.

The resultant dispersion was coagulated in an apparatus as also used forExamples 5 to 7 and described there with reference to FIG. 6. Theexperimental results are given in Table 4 together with the respectiverotation rate of the rotor 209.

TABLE 4 Experiment Rotation No. Gap width rate Throughput Remarks 14 0.5mm 1180 rpm 21 kg/h coagulation 15 0.5 mm 2420 rpm 18 kg/h coagulation16 0.5 mm 3660 rpm 20 kg/h coagulation 17 0.5 mm  980 rpm 110 kg/h incomplete coagulation

EXAMPLE 18

Preparation of another Graft-rubber Dispersion with Polybutadiene asGraft Base

60 parts of butadiene were polymerized at 65° C. to a monomer conversionof 98% in a solution of 0.6 parts of tert-dodecyl mercaptan, 0.7 partsof sodium C₁₄-alkylsulfonate as emulsifier, 0.2 parts of potassiumperoxodisulfate and 0.2 parts of sodium bicarbonate in 80 parts ofwater. The polybutadiene in the resultant latex had an average particlesize of 100 nm and was therefore agglomerated by adding 25 parts of a10% strength emulsion of a copolymer made from 96% of ethyl acrylate and4% of methacrylamide, whereupon the average particle size became 350 mm.The glass transition temperature of the polybutadiene is −85° C.

To the product were added 40 parts of water, 0.4 part of sodiumC14-alkylsulfonate and 0.2 part of potassium peroxodisulfate.

40 parts of a mixture of 70% of styrene and 30% of acrylonitrile wereadded gradually within a period of 4 hours, and the mixture was held at75° C., with stirring. The monomer conversion was practicallyquantitative. The glass transition temperature of a copolymer made from70% of styrene and 30% of acrylonitrile is about +105° C.

The resultant dispersion was coagulated by the novel process in anapparatus shown in FIG. 7. The figures used to indicate features of theapparatus in FIG. 7 which are comparable with those in FIG. 1 are higherby 300 than those in FIG. 1.

The feed zone 310 here is composed of the single-flight conveying module302. Attached to the feed zone 301 is the shearing module 303. This,however, is not composed of a smooth stator 307 and rotor 309 but has astator-rotor combination 307, 309 in which the stator 307 is a toothedwheel and is composed of rows of teeth in a circular arrangementradially around the rotor shaft, no further detail of which is given.The rotor 309 is composed of radial rows 313 of teeth which arecomplementary to the rows of teeth on the stator 307 and have astar-shaped arrangement around the axis of rotation of the apparatus.The stator 307 and the rotor 309 here intermesh so as to form a gap 311not expressly shown in FIG. 7, with a gap width of 0.5 mm.

Attached to the shearing module 303 there is the metering zone 305, inthe form of a double-flighted conveying screw.

Here, as in the embodiments described above of the novel apparatus,there may, if desired, be feed lines 317, 317′, 317″ in the feed zone301, in the shearing module 303 and/or in the metering zone 305, forsolvents, such as water, and/or additives. The feed lines 317′, 317″ arenot included in FIG. 7 for reasons of clarity.

The rotation rate of the rotor 309 was set at about 8000 rpm. With athroughput of 240 kg/h complete coagulation of the dispersion describedwas achieved, with problem-free running of the apparatus. After theexperiment had ended, residual dispersion could no longer be detected inthe product. This confirms that precipitation is complete.

EXAMPLE 19

Precipitation of a Plastics Dispersion by Shear

A dispersion made from poly(n-butyl acrylate-co-styrene) withstyrene/n-butyl acrylate=50/50, solids content=39.1%, particle sized₅₀=182 nm, was precipitated in the apparatus described in Examples 10to 13.

TABLE 5 Experiment Gap width Rotation rate Remarks 18 1 mm 4400 rpmcoagulation

EXAMPLES 20 TO 24

The graft-rubber dispersions mentioned in Examples 14 to 17 withelastomeric polyacrylate as graft base were also coagulated using themodified apparatus shown diagrammatically in FIG. 8 and described below.

The details given below are therefore essentially the changes in theconstruction of the apparatus. The figures used to indicate features ofthe apparatus in FIG. 8 which are comparable with those in FIG. 1 arehigher by 400 than those in FIG. 1.

A significant difference which should be mentioned between theembodiment of the novel apparatus as in FIG. 1 and the modification asin FIG. 8 is that the precipitation of the particular plasticsdispersion or rubber dispersion and its conveying through the shearingapparatus take place together and simultaneously in a shearing module403, composed of a fixed cylindrical stator 407 and of a rotor 409 inthe form of a screw, where the diameter of the screw root increases inthe direction of conveying, and is 93,5-105 mm as far as this embodimentis concerned. The diameter of the bar, or crosspiece, i.e. theunbevelled part of the screw, is 109,5 mm, and the screw has a tength of110 mm. The gap 411 formed between the stator 407 and the rotor 409,with a predetermined defined gap width, is therefore determined in thisworking example by the flight depth of the screw. Since the diameter ofthe screw root increases in the direction of conveying it follows thatthe predetermined gap width and, respectively, the flight depth, of suchan arrangement showing a screw with an increasing root, decreases in thedirection of conveying.

In this working example, the dispersion to be coagulated is passedradially by way of the feed line 412′ into the shearing module 403. Aspreviously in Working Example 1, the dispersion is added via an externalconveying system, no further detail of which is given in FIG. 8, or withthe aid of static pressure. If desired, there are points for measuringpressure and/or temperature in the shearing zone formed by the shearingmodule 403. Each of these is indicated in FIG. 8 by P forpressure-measurement point(s) and T for temperature-measurementpoint(s). The diameter of the shearing apparatus was 110 mm.

TABLE 6 Experiment No. Rotation rate Throughput Remarks 20 1000 rpm 600kg/h complete coagulation 21 2000 rpm 1000 kg/h  complete coagulation 222700 rpm 1100 kg/h  complete coagulation 23 1300 rpm 500 kg/h completecoagulation 24 1700 rpm 800 kg/h complete coagulation

We claim:
 1. An apparatus for essentially salt-free coagulation ofplastics dispersions or rubber dispersions, comprising at least oneshearing module (3, 103, 103′, 203, 303, 403) said shearing modulehaving a stator (7, 107, 207, 307, 407) and a rotor (9, 109, 109′, 209,309, 409) arranged within the said stator (7, 107, 207, 307, 407) wherethe surfaces facing toward one another in the said stator (7, 107, 207,307, 407) and in the said rotor (9, 109, 109′, 209, 309, 409) are ineach case smooth, or at least the said rotor exhibits a structure formedon its surface and facing from this in the direction of the said stator(7, 107, 207, 307, 407) and between the said stator (7, 107, 207, 307,407) and the said rotor (9, 109, 109′, 209, 309, 409) there is a gap(11, 111, 111′, 211, 311, 411) of predetermined width.
 2. The apparatusas claimed in claim 1, wherein the diameter or the rotor (9, 109, 109′,209, 309, 409) decreases or increases in the direction of conveying. 3.The apparatus as claimed in claim 1, wherein the predetermined gap widthdecreases in the direction of conveying.
 4. The apparatus as claimed inclaim 1, wherein the rotor (9, 109, 109′,209, 309) has toothed-wheelstructure, the rows (13, 313) of teeth in which have a circulararrangement radially around the rotor (9, 109, 109′, 209, 309).
 5. Theapparatus as claimed in claim 1, wherein the rotor (9, 109, 109′, 209,309) has a toothed-wheel structure, the rows (13, 313) of teeth in whichhave a circular arrangement radially around the rotor (9, 109, 109′,209, 309) and the teeth on the rotor (9, 109, 109′, 209, 309) areapproximately rectangular.
 6. The apparatus as claimed in claim 1,wherein the rotor (9, 109, 109′,209, 309) has a toothed-wheel structure,the rows (13, 313) of teeth in which have a circular arrangementradially around the rotor (9, 109, 109′, 209, 309) and the rows (13,313) of teeth on the rotor (9, 109, 109′,209, 309) have an approximatelystar-shaped arrangement.
 7. The apparatus as claimed in claim 1, whereinthe rotor (9, 109, 109′,209, 309) has a toothed-wheel structure, therows (13, 313) of teeth in which have a circular arrangement radiallyaround the rotor (9, 109, 109′, 209, 309) and there is a helicalarrangement of teeth.
 8. The apparatus as claimed in claim 1, whereinupstream and/or downstream of the shearing module (3, 103, 103′, 203,303) there is a conveying screw with one or more flights.
 9. Theapparatus as claimed in claim 1, wherein the gap width is from 0.05 to20 mm.
 10. The apparatus as claimed in claim 1, wherein the shearingmodule (403) is a screw module, the screw of which forms the rotor(409).
 11. A process for essentially salt-free coagulation ofdispersions using the apparatus as claimed in claim 1, in which thedispersion is passed through the gap (11, 111, 111′, 211, 311, 411)between stator (7, 107, 207, 307, 407) and rotor (9, 109, 109′, 209,309, 409) and is precipitated by rotation of the rotor (9, 109, 109′,209, 309, 409) with a predetermined shear rate and shear deformation.12. The process as claimed in claim 11, wherein the shear rate is fromabout 100 to 100,000 s⁻¹ and the shear deformation is from about 1 to100,000.
 13. The process as claimed in claim 11, wherein the rotor (9,109, 109′, 209, 309, 409) rotates at a rotation rate of from about 50 to10,000 rpm.
 14. The process as claimed in claim 11, where thedispersions are polymer dispersions or graft-rubber dispersions.
 15. Theprocess as claimed in claim 13, wherein the rotor (9, 109, 109′, 209,309, 409) rotates at a rotation rate of from 200 to 8000 rpm.